1. Field of the Invention
The present invention relates to a welding method for forming a chromium oxide passivated film at a welded portion, as well as to a welding apparatus and a process apparatus.
2. Description of Related Art
The pace of the development of semiconductor devices having high LSI and high performance has increased greatly, and manufacturing apparatuses which are capable of producing such semiconductor devices have been in demand, and energetic efforts have been made to produce atmospheres having a higher degree of vacuum and higher cleanliness.
In order to produce atmospheres having an ultra-high degree of vacuum and having ultra-high cleanliness, it is necessary to completely suppress the release of gas from the apparatus as well as from the gas supply piping system. As a result of diligent research efforts by the present inventors over a period of many years, a chromium oxide passivated film treatment method has been perfected, so that it has become possible to form, on a surface, an oxide passivated film having chromium oxide as a chief component thereof, which is corrosion resistant and non-catalytic, and which furthermore restricts gas release in the extreme. As a result, the present inventors have succeeded in producing an atmosphere in which the release of gas from the internal portions of the apparatus is restricted to an amount which is difficult to detect with present measuring devices.
However, as such apparatuses have become larger in scale, and as the complexity thereof has increased, it has become increasingly necessary to connect pipes or apparatuses by means of welding after the formation of the chromium oxide passivated film. Because the surface of the welded portions is not covered by a chromium oxide passivated film, gas easily adsorbs thereto and desorbs therefrom, and as the number of welds increases, the gas which is released therefrom reaches a level which is impossible to ignore, so that a new problem is generated in that the atmosphere becomes contaminated.
Furthermore, in apparatuses or piping systems employing corrosive gasses or the like, there are problems in that the welded portions are corroded, and as a result of this, the atmosphere becomes contaminated. The formation of an oxide passivated film in apparatuses or piping systems which are large-scale and have complicated forms requires a complex passivated film formation apparatus, and in particular in view of increasing costs, a welding method in which a passivated film can be formed simultaneously with welding has been strongly desired.
In view of the above points, the present invention has as an object thereof to provide a welding method which is capable of forming an oxide passivated film, which is corrosion resistant and non-catalytic and which releases extremely little gas, at welded portions and at the vicinity thereof during the welding process. Furthermore, the present invention has as a further object thereof to provide a process apparatus requiring an extremely clean atmosphere.